US20060059796A1

US20060059796A1 - Energy absorber and method of forming the same

Info

Publication number: US20060059796A1
Application number: US10/941,159
Authority: US
Inventors: Atle Gjelsvik
Original assignee: VESCOM STRUCTURES Inc
Current assignee: SMI PATENT HOLDINGS GROUP LLC
Priority date: 2004-09-15
Filing date: 2004-09-15
Publication date: 2006-03-23
Also published as: CA2516209A1

Abstract

An energy absorber particularly for an earthquake resistant building including one or more ductile members, and two or more bracing members that support the one or more ductile members, wherein, when a force is applied to the energy absorber, the one or more ductile members deform to absorb energy.

Description

FIELD OF THE INVENTION

The present invention relates to energy absorbers, and in particular to energy absorbers for earthquake resistant buildings.

BACKGROUND OF THE INVENTION

Earthquakes exert lateral and vertical forces on a building, and fabricating a structure that will withstand these random, often sudden forces is a complex task. When designing an earthquake-resistant building, engineers can choose various structural components, such as shear walls, braced frames, moment resisting frames, diaphragms and horizontal trusses. These building elements impart earthquake resistant structures with the ability to resist and sometimes to absorb and dissipate seismically induced motion through a combination of means, including damping means which absorbs energy and decreases the amplitude of oscillations of a vibrating structure and inelastic deformation means which can withstand considerable inelastic deformation. The structural elements can be used alone or in combination to achieve the necessary energy absorption and dissipation.
There are many known supporting structures having ring-like or cylindrical elements that are used to make a building earthquake resistant. For example, U.S. Pat. No. 981,824 to Veres shows diagonal braces connected between upright columns and a cylindrical post and secured to the cylindrical post with adjustable nuts. U.S. Pat. No. 5,605,021 to Thomann describes an earthquake-proof building which includes circular rings supporting circular dish elements. However, the purpose of the known ring-like supporting structures discussed above is to enhance the rigidity of a building so that the building acts as a unit during an earthquake. U.S. Pat. No. 5,097,547 to Tanaka et al. discloses a vibration absorption device which comprises outer and inner rings interconnected by radial spokes. The deformation of the radial spokes due to rotation of the outer ring relative to the inner ring during application of a vibratory force results in absorption of energy.
Accordingly, there is a need for a deformable part of a supporting structure that can absorb energy and easily reverse its load-bearing capacity, particularly for use in imparting requisite earthquake resistance to a building.

SUMMARY OF THE INVENTION

An energy absorber according to an exemplary embodiment of the invention includes one or more ductile members and two or more bracing members that support the one or more ductile members. When a force is applied to the energy absorber, the one or more ductile members deform to absorb energy. In one embodiment of the invention, the one or more ductile members are ductile rings.
A particular application for the energy absorber of this invention is incorporation in a building to impart earthquake resistance to the building. The energy absorber according to this exemplary embodiment of the invention includes at least one ductile ring adapted to be disposed within a panel member of a structural element of the building, and tension rods each of which includes a first end connected to the at least one ductile ring and another end adapted to be connected to the panel member, wherein the ductile ring is disposed at substantially the center of the panel member. The structural element can be, for example, a shear wall or part of a truss and the panel member can be, for example, rectangular.
An energy absorber according to another exemplary embodiment of the invention includes a panel member that is attachable to a structural element of a building, at least one ductile ring disposed within the panel member, and at least two bracing members that connect the at least one ductile ring with the panel member.
In one embodiment of the invention, a plurality of ductile rings are disposed adjacent to one another.
In another embodiment of the invention, a plurality of ductile rings are nested within one another, and energy absorbing material may be disposed between the rings.
The invention also encompasses a method of forming an energy absorber for an earthquake resistant building, including connecting respective first ends of two or more bracing members to one or more ductile members, disposing the one or more ductile members within an opening of a structural element of the building, and connecting respective second ends of the two or more bracing members to the structural element of the building.

BRIEF DESCRIPTION OF THE DRAWINGS

Various exemplary embodiments of this invention will be described in detail, with reference to the following figures, wherein:
FIG. 1 illustrates an energy absorber according to an exemplary embodiment of the invention within a panel member installed in a building;
FIG. 2 is a detailed view of the energy absorber of FIG. 1 within a panel member;
FIGS. 3 and 4 illustrate the operation of an energy absorber according to an exemplary embodiment of the invention during application of shear forces to the panel member;
FIG. 5 is a load-deformation curve for an energy absorber according to an exemplary embodiment of the invention during cyclic loading;
FIG. 6 shows an energy absorber according to another exemplary embodiment of the invention;
FIG. 7 shows a partially cut away view of an energy absorber according to another exemplary embodiment of the invention;
FIG. 8 shows an energy absorber according to another exemplary embodiment of the invention;
FIG. 9 shows a partially cut away view of an energy absorber according to another exemplary embodiment of the invention;
FIG. 10 shows an energy absorber according to an exemplary embodiment of the invention in which a ductile ring is made of four portions; and
FIG. 11 shows an energy absorber according to an exemplary embodiment of the invention including a diamond-shaped ductile member.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The various exemplary embodiments of the present invention are directed to an energy absorber that imparts buildings with the ability to withstand forces caused by, for example, earthquakes. It should be appreciated that the various concepts of the present invention are not necessarily limited to earthquake resistant structures, but are also applicable to structures that are designed to withstand forces generated by any other factor, such as, for example, explosions or high winds.
FIG. 1 illustrates an energy absorber 4 according to an exemplary embodiment of the invention used in a building 1. According to the present embodiment of the invention, the energy absorber 4 is located in an opening 3 in a structural member of a building, such as shear wall 2. However, it should be appreciated that the present concept is not limited to shear walls, and the energy absorber 4 can be applied to any other structural element of a building, such as, for example, a truss or a joist. Further, the energy absorber 4 need not be disposed vertically within the building 1, but can be disposed oriented in any direction which would maximize force-absorption.
FIG. 2 is a more detailed view of an embodiment of the energy absorber 4 of FIG. 1. As shown in FIG. 2, the energy absorber 4 includes a ductile member 6, four braces 8 and four frame members 10 which form structural panel 5. The braces 8 support the ductile member 6 at substantially the center of the structural panel 5. The ductile member 6 is formed of a ductile material, such as, for example, steel or aluminum. One of the ends of the braces 8 are connected to the ductile member 6 by any suitable fastening elements, such as, for example, adjustable nuts 12. The opposite ends of the braces 8 are attached to respective corners of the structural panel 5 by, for example, pin joints, welding or bolts. The number of braces 8 is not limited to four and any number of braces 8 can be used in the various exemplary embodiments of the invention. In the present embodiment of the invention, the braces 8 are tension rods, but can also be any other suitably rigid structural supports for the ductile element 6. Further, the ductile member 6 need not be ring-shaped, as shown in FIG. 2, but could have other shapes as would be understood by workers skilled in the art. Furthermore, structural panel 5 is not limited to a rectangular shape and can take other shapes, such as, for example, circular. For convenience, the present invention will be described below with reference for the most part to a circular ductile ring.
The energy absorber in accordance with FIG. 2 is modular in nature, that is, prefabricated, and the structural panel 5 is combined with a shear wall or other structural element during construction of the building. For example, the entire energy absorbing structural panel 5 shown in FIG. 2 may be prefabricated to include the energy absorber 4 before placement of the panel into the shear wall 2. Prefabrication of the structural panel 5 allows for more easy transport to the construction site and placement into structural elements of the building. However, the energy absorber 4 can also be a separate element that can be placed into an opening in the shear wall 2 without the frame members 10.
FIGS. 3 and 4 illustrate the operation of the energy absorber 4 during application of shear forces to the structural panel 3. As shown in FIG. 3, the application of shear force F1 to the structural panel 3 causes a deformation y so that one diagonal of the panel 3 increases in length and another diagonal of the panel 3 decreases in length. The deformation of the structural panel 3 causes the ring 6 to deform into an oval in a ductile manner so that the braces 8 will tend to stay in tension. This causes absorption of energy, or, put another way, substantially reduces the transfer of such energy through the remainder of the building 1 to prevent or diminish structural damage to the building 1 during an earthquake or other disaster. As shown in FIG. 4, when the shear deformation is reversed by a shear force F2, the ovalization of the ring is reversed, again tending to keep the braces 8 in tension. As can be seen in FIGS. 3 and 4, the ring structure of the energy absorber 4 minimizes or substantially eliminates buckling and/or slacking of the braces 8 upon shear reversal, which would normally occur if no such ring structure was present.
FIG. 5 is a load-deformation diagram which generally illustrates the deformation of the structural panel 3 during application of a shear force F that causes a deformation y. For each cycle of loading, the corresponding point in the load-deformation curve A traces out a loop representing energy absorption. The shaded region B represents the total amount of energy absorbed during the load cycling. When the structural panel 3 is subjected to shear forces, the resulting shape of the load-deformation diagram takes on a near ideal form. As can be seen from the hysteretic load-deformation curve A, the energy absorber of the present invention can maintain nearly all of its strength and stiffness over a number of large cycles of inelastic deformation. The resulting force-deformation “loops” are quite wide and open, showing a large amount of energy dissipation capacity.
FIG. 6 shows an energy absorber according to another exemplary embodiment of the present invention. The energy absorber 20 according to that embodiment of the present invention includes a first ductile ring 22, a second ductile ring 24 and four braces 26. The first ductile ring 22 is disposed adjacent to, but spaced from, the second ductile ring 24, so that an opening 23 is formed between the first ductile ring 22 and the second ductile ring 24. As shown in FIG. 6, each of the braces 26 include a T-shaped end welded or otherwise bonded to the first and second ductile rings 22 and 24 so that each of the braces 26 protrude from the opening 23 between the first and second ductile rings 22 and 24. The opposite ends of the braces 26 are attached to respective corners of a structural panel by, for example, pin joints, welding or joints. As in other embodiments of the invention, the number of braces 26 is not limited to four. Further, the number of ductile rings is not limited to two, but can be any number of ductile rings disposed adjacent to one another. The plural ductile ring structure of the present embodiment allows for easier connection of the ductile rings to the diagonal braces and provides additional energy absorption compared to the single ductile ring structure.
FIG. 7 shows a partially cut away view of an energy absorber according to another exemplary embodiment of the invention. The energy absorber 30 according to that embodiment of the invention includes a first ductile ring 32, a second ductile ring 34 and two braces 36. The first ductile ring 32 has a smaller diameter than the second ductile ring 34, and is placed inside, or “nested” with, the second ductile ring 34. It should be appreciated that the number of nested rings is not limited to two, and any number of such rings having different diameters can be nested together. The first ductile ring 32 and second ductile ring 34 are preferably nested in contact with one another. Two slotted openings 33 are formed on the side portions of the first ductile ring 32, and corresponding two slotted openings 35 are formed on the side portions of the second ductile ring 34. Each of the braces 36 extends through respective slotted openings 33 and 35 in the first and second ductile rings 32 and 34, and are fastened to the first and second ductile rings 32 and 34 by, for example, adjustable nuts 38. When a shear force is applied to the energy absorber 30, the first and second ductile rings 32 and 34 deform into an oval shape. The slotted openings 33 and 35 allow the first and second ductile rings 32 and 34 to rotate and slide over one another during their respective deformation. Frictional forces caused by the relative motion of the first and second ductile rings 32 and 34 result in additional energy absorption.
FIG. 8 shows an energy absorber according to another exemplary embodiment of the invention. The energy absorber 40 of that embodiment of the invention has substantially the same structure as the previous embodiment except for the shape and connection of the braces. The energy absorber 40 includes a first ductile ring 42 nested within a second ductile ring 44. Each of two braces 46 includes a T-shaped end that is welded or otherwise bonded to the second ductile ring 44. Frictional forces between the first and second ductile rings 42 and 44 during application of shear force to the energy absorber 40 results in increased energy absorption.
FIG. 9 shows a partially cut away view of an energy absorber according to yet another exemplary embodiment of the invention. That embodiment is substantially the same as the embodiment shown in FIG. 7 except that the first and second ductile rings 32 and 34 are separated by an energy absorbing material 50. That is, rather than being in contact with one another as in the previous embodiment, the first and second ductile rings 32 and 34 are spaced apart with an energy absorbing material 50 disposed between them. The energy absorbing material 50 may be, for example, any foam or gel-like substance that can be injected between the first and second ductile rings 32 and 34 or preformed in a ring structure to fit between the first and second ductile rings 32 and 34.
The means of attaching the braces to the ductile ring described in the previous embodiments of the invention are merely exemplary, and any suitable fastening configuration and structure can be used. For example, FIG. 10 shows an energy absorber 60 according to an exemplary embodiment of the invention in which a ductile ring 62 is made of four portions. A brace 64 extends between each of the portions and is bolted to the ductile ring 62 by, for example, adjustable nuts 66.
As previously mentioned, the ductile member in various exemplary embodiments of the invention is not limited to a circular shape. For example, FIG. 11 shows an energy absorber 70 including a diamond-shaped ductile member 72. The ductile member 72 can be formed of four portions. A brace 74 extends between each of the portions and is bolted to the ductile member 72 by, for example, adjustable nuts 76. It should be appreciated that the diamond-shaped ductile member can be attached to the braces by any other suitable means, such as by means described in previous embodiments with reference to a circular ductile member. Further, multiple diamond-shaped ductile members can be nested together or disposed next to each other to enhance energy absorption.
While this invention has been described in conjunction with the exemplary embodiments outlined above, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the exemplary embodiments of the invention, as set forth above, are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention.

Claims

1. An energy absorber comprising:

one or more ductile members; and

two or more bracing members that support the one or more ductile members, wherein, when a force is applied to the energy absorber, the one or more ductile members deform to absorb energy.

2. The energy absorber according to claim 1, wherein the one or more ductile members are ductile rings.

3. The energy absorber according to claim 1, wherein the one or more ductile members are diamond-shaped.

4. The energy absorber according to claim 1, wherein the one or more ductile members comprise a plurality of ductile rings disposed adjacent to one another.

5. The energy absorber according to claim 1, wherein the one or more ductile members comprise a plurality of ductile rings nested within one another.

6. The energy absorber according to claim 5, wherein the plurality of ductile rings are in contact with one another.

7. The energy absorber according to claim 5, wherein an opening is formed between at least one of the plurality of ductile rings and an adjacent one of the plurality of ductile rings, and an energy absorbing material is disposed in the opening.

8. The energy absorber according to claim 5, wherein one or more slotted openings are formed in each of the one or more ductile rings, and each of the two or more bracing members is connected to the plurality of ductile rings through a respective one of the one or more slotted openings.

9. The energy absorber according to claim 1, wherein the two or more bracing members are tension rods.

10. The energy absorber according to claim 9, wherein each of the tension rods has a T-shaped end attached to the one or more ductile members.

11. An energy absorber for an earthquake resistant building comprising:

at least one ductile ring adapted to be disposed within a panel member of a structural element of the building; and

tension rods each of which includes a first end connected to the at least one ductile ring and another end adapted to be connected to the panel member, wherein the ductile ring is disposed at substantially the center of the panel member.

12. An energy absorber for an earthquake resistant building comprising:

a panel member that is attachable to a structural element of the building;

at least one ductile member disposed within the panel member; and

at least two bracing members that connect the at least one ductile member with the panel member.

13. The energy absorber according to claim 12, wherein the at least one ductile member is a ductile ring.

14. The energy absorber according to claim 12, wherein the at least one ductile member is diamond-shaped.

15. The energy absorber according to claim 12, wherein the panel member is rectangular.

16. The energy absorber according to claim 12, wherein the at least two bracing members comprise four bracing members, each of the four bracing members including a first end connected to the at least one ductile member and another end adapted to be connected to a respective corner of the panel member.

17. A method of forming an energy absorber for an earthquake resistant building comprising:

connecting respective first ends of two or more bracing members to one or more ductile members;

disposing the one or more ductile members within an opening of a structural element of the building; and

connecting respective second ends of the two or more bracing members to the structural element of the building.

18. The method according to claim 17, wherein the one or more ductile members are ductile rings.

19. The method according to claim 17, wherein the one or more ductile members are diamond-shaped.